A copper phthalocyanine is an organic pigment of a blue or a cyan color widely used in a coating material, an ink jet ink, a color filter, a toner, and so on. A metal-free phthalocyanine having central copper replaced with hydrogens in its molecular structure and many kinds of metal phthalocyanine having central copper replaced with other metal elements in its molecular structure have been synthesized; however, among them, a copper phthalocyanine is largest in its industrial use because it is excellent not only in color characteristics such as a coloring power and a color-producing power as a color material but also in water resistance, heat resistance, and durability such as light resistance and weatherability. A copper phthalocyanine is also used for a semiconductor, a catalyst, a sensor, and so on, in addition to the organic pigment and the color material as mentioned above, so that this compound is also considered to become an important material from now on.
A copper phthalocyanine has many crystal polymorphisms such as α, β, γ, ε, π, χ, σ, and ρ; and it is said that a copper phthalocyanine is different in physical properties such as color characteristics and solvent resistance depending on its crystal type. However, color characteristics of a copper phthalocyanine is significantly influenced not only by its crystal type but also by a diameter of its primary particles and degree of agglomeration during its use, in other words, it is also influenced by a diameter of dispersed particles; and thus, a producing method in accordance with the intended crystal type thereof is required, so that many methods for controlling the crystal type and for producing microparticles have been reported.
As to the production method of, for example, the β- or the ε-type copper phthalocyanine, reported are: a solvent method in which treatment thereof is done with specific organic solvents such as those described in Patent Document 1; and a so-called solvent milling method and solvent salt milling method in which treatment with beads or an inorganic salt is done in specific solvents such as those described in Patent Document 2.
However, in the solvent method, control of formation of large particles due to crystal growth is difficult; and in the solvent milling method and the solvent salt milling method, crystal growth and crushing of crystals occur in parallel, so that there have been problems of not only requiring large energy but also not expressing characteristics expected as pigment nanoparticles, such as color tone, transparency, spectroscopic characteristics, and durability, because a strong force is applied to the copper phthalocyanine.
The Applicant of the present invention proposed, in Patent Document 3, a copper phthalocyanine pigment and a method for producing the same, wherein the copper phthalocyanine pigment contains a novel copper phthalocyanine having the α-type crystal structure with a wavelength (λmax) to give the maximum transmittance in 380 nm to 780 nm of its transmission spectrum being shorter than 478 nm. The copper phthalocyanine shown in Patent Document 3 has excellent transmission characteristics and can transmit light of a specific wavelength range, while the transmittance thereof is higher than ever. In addition, in its absorption spectrum characteristics, its absorbance is higher as compared with a general copper phthalocyanine even if its dispersion solution thereof has the same concentration as the latter; and thus, it can be assumed that a coloring power thereof is better as compared with existing copper phthalocyanine pigments. However, there has been a problem that the α-type crystal thereof, which is generally considered to be quasi-stable, grows in a certain solvent especially when attempt is made to use it in an aromatic organic solvent thereby not expressing its color characteristics; and thus, a stable or a quasi-stable copper phthalocyanine which has spectroscopic characteristics as shown in the Patent Document 3, while the crystal type thereof is different from the α-type crystal, has been wanted.    Patent Document 1: Japanese Patent Laid-Open Publication No. 2003-313456    Patent Document 2: Japanese Patent Laid-Open Publication No. 2007-332317    Patent Document 3: International Patent Laid-Open Publication No. 2010/035861